1. Field of the Invention
The present invention relates to a battery state monitoring circuit that monitors a state of a battery in a battery device that is connected with a charger or a load, and a battery device that is equipped with the circuit.
2. Description of the Related Art
As a conventional battery device, there has been known a battery device shown in FIG. 2. FIG. 2 shows a conventional battery state monitoring circuit and a circuit block of the battery device.
A battery state monitoring circuit 202 includes an over-charge detecting circuit 108, an over-discharge detecting circuit 107, an over-current detecting circuit 108, and a logic circuit 305.
In the battery state monitoring circuit 202, when a given condition is satisfied, the logic circuit 305 outputs a high signal in order to turn on an FET 304 and an FET 303 within a switch circuit 203 (this state is called “normal state”).
Also, when a charger 301 is connected between an external terminal (+V0) 204 and an external terminal (−V0) 205, charging is started, and a voltage across a battery 201 exceeds a chargeable upper limit voltage, an over-charge detecting circuit 106 outputs a detection signal, and the logic circuit 305 outputs a low signal (charge inhibition signal) in order to turn off the FET 304 within the switch circuit 203 (this state is called “over-charge state”).
Further, when a load 302 is connected between the external terminal 204 and the external terminal 205, discharging is started, and the voltage across the battery 201 falls below a dischargeable lower limit voltage, an over-discharge detecting circuit 107 outputs a detection signal, and the logic circuit 305 outputs a low signal (discharge inhibition signal) in order to turn off the FET 303 within the switch circuit 203 (this state is called “over-discharge state”).
In the over-discharge state, because the switch circuit 203 turns off to stop the discharge current, the external terminal 205 is isolated from the power supply which is supplied from the battery 201, and pulled up to the load 302. The battery state monitoring circuit 202 detects that the external terminal 205 has been pulled up, and outputs a power-down signal that powers down the respective circuits to the respective circuits, to thereby suppress the current consumption of the battery-state monitoring circuit 202 per se to a small value (this state is called “power-down state”).
Also, when the load 302 is connected between the external terminal 204 and the external terminal 205, discharging is started, and a discharge current that flows in the switch circuit 203 increases, and a voltage at the external terminal 205 becomes equal to or higher than a given voltage, the over-current detecting circuit 108 outputs a detection signal, and the logic circuit 305 outputs a discharge inhibition signal in order to turn off the FET 303 within the switch circuit 203 (this state is called “over-current state”).
However, in the conventional battery state monitoring circuit 202 and the conventional battery device, in the case where the battery state monitoring circuit 202 is formed of an n-type substrate, voltage of the voltage detection terminal that monitors the positive voltage of the battery 201 becomes normally a substrate voltage, and respective voltages at the voltage detection terminal that monitors a negative voltage of the battery 201 and the current detection terminal that monitors the current of the battery 201 become a p-well voltage. In this case, when the charger 301 is connected to an opposite polarity in error, the voltage at the current detection terminal is higher than the voltage at the voltage detection terminal that monitors the positive voltage of the battery 201, there is a case in which the p-n junction within the semiconductor integrated circuit is in a forward direction, and the parasitic transistor is turned on to make a current flow therein. As a result, the circuit operation becomes unstable and a latch circuit within the logic circuit 305 is set in error, which may cause a power-down state. Thereafter, even if the charger 301 is correctly connected, the power-down state continues, and the battery device may not operate normally.